Process for producing synthetic camphor



Patented Jan. 15, 1935 UNITED V 1,987,750 PROCESS "FOR 1 PRODUCINGSYNTHETIC CAMP Hon

John J. Bitter, Yonkers, N.

No Drawing.

Application August 3, 1933 Serial 688,547 I I This invention relates toa -process.-=-for pro- .ducing synthetic camphor.

An object of the "invention is the provision-of a process forproducingsynthetic camphor. from 5 bornyl chloride, in which the bornylchloride is :treated with aniline in the presence ofxan initial quantityof camphene toproduce isobornylanilin'e. I Another object 'of' theinvention'is'lthe'provir sion of a processfor producing synthetic cam:--phor, in whichzisobornylaniline is first produced and thendehydrogenated, thereby v producing .camphor anil, steps being taken tol-obtain the pure :anil which .is then hydrolyzed tomcarnphor andaniline. q

.Another object of the invention isthe provi; sion of a process ,forproducing synthetic cam,- phor, in which isobornylaniline is firstproduced and then mixed with sulfur and heated to cause.dehydrogenation'of the isobornylaniline with the discharge of hydrogensulfide, thereby producing ,carnphor anil,. s'tep's being taken'toobtain the pure vani-l which is then hydrolyzed to camphor and aniline.e

Astillfurtherobject of the inventionis to provide a process for theproduction of synthetic eamphor by the use of nickel, las afoatalyst toeffect the dehydrogenation of isobornylaniline, therebyproducingcamphonanil which is thenhyd'rolyzed to'camphor and aniline.

This invention will be best understood from a consideration of thefollowing detailed description forming a part of the specification;nevertheless, it is to be understood that the invention is not confinedto the disclosure, being susceptible of such changes and modificationswhich shall define nomaterial departure from the salient features of theinvention as expressed in the appended claims.

It has been known that the treatment of bornyl chloride with anilineyields some isobornylaniline, together with camphene and anilinehydrochloride. This reaction is of no economic importance because theyield of-isobornylaniline. is low, and also because of the fact thatisobornylaniline has not been shown'heretofore as being capable ofconversion to'camphor inany simple manner. It is also known thattreatment of camphene with a mixture of aniline andaniline hydrochlorideproduces some isobornylaniline, but the yields of isobornylaniline arelikewise low in this reaction. It has further been known that the actionof aniline hydrochloride on iso- I have now found that mixtures ofaniline, cam--' phene, aniline hydrochloride, :and isobornylaniline cometo equilibrium, the equilibrium concentrations depending, at a giventemperature, upon, the initial concentrations of each. Therefore,

' isobornylaniline are fbornyl- Chloride treatedwith a mixture ofcamphene, aniline, andeaniline hydrochloride in which the concentrationsof the latter are so chosen to be in equilibrium,at theend of thereaction, with a concentration of isobornylaniline equivalent to thebornyl chloride used, will come 'to equilibrium in whichone equivalentof iso bornyl-aniline is produced from each equivalent of :bornylchloride, 1, e, the yield is 100%. In practice, this comprises treatmentof bornyl chloride with aniline incthe' presence of an initial quantityof camphene. ,After the reaction iscomplete, camphene equalinamou-nt tothat initially ,added may be recovered and reused indefinitely.

It isevident, from the foregoing, that high-yields of isobornylanilinemay beobtained by equilibrating mixtures of the reactants; in variousproportions;- the examplesto be given presently have been selected-froma number ofequallyeffective mixtures in different proportions.

Atypical procedure for carrying out the process will now be described:111.8 parts by weight of bornyl chloride, 47.6 :parts, by weight of.camphene, 45.4 parts by weight 'of aniline hydrochloride, and-339.4parts by weight of ,anilin'e are mixed and boiled for seven hours. Thereaction mixture is then allowed to cool, and neutralized by adding aexcess of an -galkali, such as sodium hydroxide.

An oily laye r consisting of aniline, camphene, and isobornylanilineseparates out. The aniline and camphene are separated from theisobornylaniline in any suitable manner, as by steam distillation, sinceisobornylaniline is very slightly volatile with steam. The oily layermay also be dried and distilled at ordinary pressure or in vacuo toremove the camphene and aniline. Distilation up to 130 C. at thepressure of 1 millimeter of mercury removes 47.6 parts by weight ofcamphene and 279 parts by weight of aniline. The remaining distillateconsists entirely of isobornylaniline which boils at 131 C. at thepressure given above, and 148.8 parts by weight of obtained. Therecovered .camphene and aniline may be reused indefinitely,

for the production of further quantities of isoweight of bornyl chlorideare mixed and boiled for seven hours. The reaction mixture is thenallowed to cool somewhat, and neutralized by washing with an excess ofan alkali, such as sodium hydroxide. An oil is obtained, which ondistillation as described in the previous example yields 238 parts byweight of aniline, '16 parts by weight of camphene, and 100 parts byweight of isobornylaniline. To the recovered aniline (238 parts byweight) and camphene ('76 parts by Weight) are now added '76 parts byweight of bornyl chloride and 41 parts by weight of aniline for theproduction of a further 100 parts by weight of isobornylaniline.

Two methodsfor the production of isobornylaniline have been described,and it is immaterial which method is used for the next step of theprocess, which is the production of camphor anil. In this step, 100parts by weight of isobornylaniline is mixed with 14 parts by weight ofsulfur, and the mixture heated at temperatures ranging from 190 C. to300 C. approximately, to efiect dehydrogenation of theisobor'nylaniline. This may be accomplished, for example, by heating at215-220 C. for two hours, and then raising the temperature to 230-235C., where the heating is continued for an additional two hours. Thecamphor anil is now separated from the crude reaction mixture bydistillation or other convenient means. Distillation at the pressure of1 mm. of mercury yields 75 parts by weight of camphor anil boiling at118120 C., and 15 parts by weight of unchanged isobornylaniline.

The camphor anil is now hydrolyzed to camphor and aniline. This may beaccomplished by any customary method of hydrolysis. One such method isas follows: The camphor anil is added to a slight excess of mineralacid, such as sulfuric acid, in approximately 25% aqueous solution, andheated at -100 C. for one-half hour. The camphor is then isolated in anywell known manner.

I have previously explained how isobornylaniline may bedehydrogenatedwith sulfur, and will now describe a further process inwhich the dehydrogenation is accomplished by the action of a metalcatalyst such as nickel: parts by weight 01 isobornylaniline, 2 parts byweight of sodium hydroxide, and 10 parts by weight of nickel (obtainedin an active form by reduction of the oxide with hydrogen at 300-310 C.,or in any other well known manner) are heated at a temperature around340 C. for two hours, during which hydrogen is steadily evolved. Thepartially dehydrogenated product of this treatment is then distilled 45to separate the camphor anil formed.

Another procedure for the dehydrogenation of isobornylaniline involvesthe use of such oxidizing agents as chromic acid, permanganate, andoxygen. One procedure of this type will be outlined: isobornylaniline isheated to approximately 100-150 C., and oxygen led into the liquid for aperiod of four hours. The product of this treatment is then heated for ashort time with an aqueous solution of an acid, as sulfuric acid, and

camphor is thereby produced and may be isolated in any convenientmanner.

It is to be noted that it is not the intent, in this specification, tolimit the process described to the particular reagents and conditionsset forth in the above examples. These examples have been given toelucidate typical working procedures. In particular, it should be notedthat other bornyl halides, as the bromide, may be used in place ofbornyl chloride; and other aromatic amines, as the toluidines, may besubstituted for aniline, yielding the corresponding N-rnonoisobornylderivatives of the aromatic amines, which on dehydrogenation yield thecorresponding N-aryl camphor imines.

It has been found also that treatment of albornyl derivative of thearomatic amine to yield the corresponding N-aryl camphor imine, andhydrolysis of the latter to form camphor and the corresponding aromaticamine.

The formula is indicative of the course of reactions in carrying out myprocess:

I claim:

1. The process of producing synthetic camphor which comprises treatingbornyl chloride with aniline in the presence of aniline hydrochlorideand an initial quantity of camphene to form isobornylaniline, thenheating a mixture of the isobornylaniline and sulfur to form camphoranil, then treating the last-named compound With a water solution of anacid to form camphor and then removing the camphor.

2. The step in the process for the production of synthetic camphor whichcomprises treating bornyl chloride with aniline in the presence of aninitial quantity of camphene to produce isobornylaniline.

3. The step in the process for the production of synthetic camphor whichcomprises treating a bomyl halide with an aromatic amine in the presenceof an initial quantity of camphene to produce the correspondingN-monoisobornyl derivative of the aromatic amine.

4. The step in the process for the production of synthetic camphor whichcomprises treating alpha-pinene with a mixture of aniline and anilinehydrochloride to produce isobornyl aniline.

5. The step in the process for the production of synthetic camphor whichcomprises treating substances capable of yielding camphene on treatmentwith a mixture of an aromatic amine and an aromatic amine hydrohalidewith that mixture in the present of an initial quantity of camphene toproduce the corresponding N-monoisobornyl derivative of the aromaticamine.

6. The step in the process for the production of synthetic camphor whichcomprises treating isobornylaniline with sulfur, thereby dehydrogenatingthe isobornylaniline with the discharge of hydrogen sulfide and formingcamphor anil.

7. The step in the process for the production of synthetic camphor whichcomprises treating isobornylaniline with a nickel catalyst, therebydehydrogenating the isobornylaniline with the discharge of hydrogen andforming camphor anil.

8. The step in the process for the production of synthetic camphor whichcomprises treating the N-monoisobornyl derivative of an aromatic aminewith a nickel catalyst, thereby dehydrogenating the N-monoisobornylderivative of the aromatic amine to the corresponding N-aryl camphorimine.

9. The process for producing synthetic camphor comprising treatingsubstances capable of yielding camphene on treatment with a mixture ofan aromatic amine and aromatic amine hydrohalide with that mixture toproduce the corresponding N-monoisobornyl derivative of the aromaticamine, then dehydrogenating the latter to yield the corresponding N-arylcamphor imine, and hydrolyzing N-aryl camphor imine to yield camphor andthe aromatic amine.

JOHN J. RITTER.

